The existence of multiple anomalous U(1)s is demonstrated explicitly in a blow–up version of a heterotic Z3 orbifold. Another blow–up of the same orbifold supports further evidence for the type– I/heterotic duality in four dimensions. It has a single anomalous U(1) which does not factorize universally. As multiple anomalous U(1)s as well as non-universal factorization have never been established on heterotic orbifolds explicitely, these findings might appear contradictory at first sight… CONTINUE READING